Central endocrine glands

Question 1

Structure of hypothalamus

Answer 1

• Forms lower lateral walls and floor of the third ventricle.

Question 2

Function of hypothalamus

Answer 2

Regulate pituitary glands secretion through stimulation of tropic hormones.

Question 3

Structure of pituitary gland

Answer 3

• Attach to hypothalamus by infundibulum (with vasculature & nerve axons)
• Anterior lobe consists glandular tissue.
• Posterior lobe consists neural tissue.

Question 4

How does hypothalamus interact with anterior pituitary to release hormones?

Answer 4

Hypothalamus → Hypophyseal portal system (blood vessel system)
→ pituitary stalk → bind to anterior pituitary receptor → stimulate release of other hormones.

Question 5

How does hypothalamus interact with posterior pituitary to release hormones?

Answer 5

Hormones path: Hypothalamus → pituitary stalk → posterior pituitary via axons.

Question 6

Hypothalamus: Hormones Stimulation to anterior pituitary (7)

Answer 6

a. Gonadotropin-releasing hormone (GnRH) ⇒ ↑ FSH & ↑ LH
b. Growth hormone-releasing hormone (GHRH) ⇒ ↑ growth hormone (GH)
c. Thyrotropin-releasing hormone (TRH) ⇒ ↑ thyroid-stimulating hormone (TSH)
d. Corticotropin-releasing factor (CRF) ⇒ ↑ adrenocorticotropic hormone (ACTH)
e. Dopamine/Prolactin-inhibiting hormone (PIH) ⇒ ↓ prolactin
f. Prolactin-releasing hormone (PRH) ⇒ ↑ prolactin
g. Growth hormone-inhibiting hormone (GHIH, somatostatin) ⇒ ↓GH

Question 7

Hypothalamus: Hormone secretion to posterior pituitary

Answer 7

a. Oxytocin
b. Antidiuretic hormone (ADH)

Question 8

Anterior Pituitary: Hormones stimulation (FLAT PEG)

Answer 8

Tropic Hormones (peptide hormones)

a. FSH (gonadotropin) ⇒ ↑ spermatogenesis in male; ↑ growth of ovarian follicle in female.
b. LH (gonadotropin) ⇒ ↑ testosterone release in male; induce ovulation, formation of corpus luteum in female.
c. Adrenocorticotropic hormone (ACTH): acts on adrenal cortex ⇒ ↑ corticosteroid.
d. Thyroid-stimulating hormone (TSH): acts on thyroid ⇒ ↑ thyroxine (T4) and triiodothyronine (T3) for metabolism.

Question 9

Anterior Pituitary: Hormones stimulation (FLAT PEG)

Answer 9

Direct Hormones (peptide hormones)

a. Prolactin ⇒ ↑ Milk & induce mammary lobule-alveolar development.
b. Endorphins ⇒ ↓ Pain sensation [RECALL: opioids act on endorphin receptor]
c. Somatotropin/Growth hormone (GH) ⇒ ↑ growth of bones & muscles; ↑↑ [glucose]

Question 10

Hypothalamus-pituitary-adrenal/gonad/thyroid axis

Answer 10

• Regulated by negative feedback.
• Hormones from target gland act on anterior pituitary / hypothalamus to inhibit secretion of hormones.
• Target glands include thyroid, gonads, adrenal.

Question 11

How is hypothalamus-pituitary- adrenal/gonad/thyroid axis regulated?

Answer 11

• Stress – CRH ↑ –ACTH ↑ –corticosteroid ↑
• Stress affects the timing of menstruation
• ‘Dormitory effect’ or Menstrual synchrony maybe due to pheromones but is controversial.
• Regulation by circadian rhythm.

Question 12

Function of GH

Answer 12

• Stimulates the growth (hyperplasia and hypertrophy) of muscle, cartilage and bones.
• Regulates metabolism
• increases protein synthesis
• maintains blood glucose level: decrease uptake of glucose in peripheral tissues; increase glucose synthesis in the liver.
• Mobilizes fat store as energy: stimulate triglyceride breakdown and oxidation in adipocytes.
• Mechanism
• Direct effect via GH receptor.
• Indirect effect via IGF-I from the liver & other tissues

Question 13

Describe bone structure.

Answer 13

• Bone cells
• Osteoblasts: bone formation - Osteoclasts: bone remodeling
• Osteocytes: bone maintenance
• Chondrocytes: cartilage cells
• Matrix
• Collagen fibers
• Calcium phosphate crystals
• Nerves and blood vessels

Question 14

How bone lengthens?

Answer 14

By the expansion of epiphyseal plate.

Question 15

Describe the expansion of epiphyseal plate.

Answer 15

GH (via IGF-1) stimulates the proliferation of chondrocytes & osteoblast activity.

1. Chondrocytes undergo cell division.
2. Older chondrocytes enlarge.
3. Calcification of extracellular matrix.
4. Dead chondrocytes cleared by osteoclasts.

Question 16

How bones grow in width?

Answer 16

• Osteoblasts (bone builder) produce a matrix of osteoid and deposit calcium phosphate.
• Osteoclast (bone breaker) carry out bone resorption on the inner side of the bone.
• IGF-1 stimulates the activity of osteoblasts and osteoclasts.

Question 17

Control of GH secretion

Answer 17

• Highest during sleep.
• Stimulated by exercising, high amino acids, low fatty acids and low glucose.

Question 18

GH disorders

Answer 18

GH hyposecretion: dwarfism
GH hypersecretion: gigantism (before epiphyseal plate stops growing); acromegaly.

Question 19

Hormones important for growth (except GH)

Answer 19

• Thyroid hormone: Allow full manifestation of GH
• Androgen & Estrogen: Promotes ossification of epiphyseal plate (stop bone lengthening).

Question 20

Posterior pituitary: Hormones stimulation

Answer 20

Hormones (peptide hormones)

a. Antidiuretic hormone (ADH)/Vasopressin: responded to ↓ blood volume/↑ blood
osmolarity (hypertonicity - detected by osmoreceptors in hypothalamus)

⇒ ↑ reabsorption of H2O by kidney (stimulate insertion of aquaporins into kidney tubules membranes) ⇒ concentrated urine & ↓ urine volume, ↑ blood volume & ↑ BP (vasoconstriction) ⇒ ↓ plasma osmolarity.

b. Oxytocin ⇒ ↑ uterine contractions during childbirth (threshold conc of oxytocin receptor GPCR); ↑ milk ejection with ↑ muscle contraction of mammary alveoli; ↑ bonding behaviour. Positive feedback loop.

Question 21

Pineal gland: Hormone stimulation

Answer 21

Hormones (peptide hormones)

a. Melatonin: Controls circadian rhythm, regulates sleep & wakefulness.

Question 22

Mechanism of melatonin secretion.

Answer 22

• Secretion is controlled by suprachiasmatic nucleus (SCN) of hypothalamus.

1. special retinal ganglion cells (sRGC) detects light.
2. Melanopsin in RGCs is a circadian photopigment.
3. Melenopsin activated in response to light → triggers action potential → transmit as nerve impulse to SCN → suppress melatonin secretion.